His Legs Suddenly Felt Paralyzed. Could Intense Workouts Be the Cause?


“I can’t move my legs,” the 26-year-old man told his younger brother, who towered above him as he lay sprawled on the floor. He’d been on his computer for hours, he explained, and when he tried to stand up, he couldn’t. His legs looked normal, felt normal, yet they wouldn’t move.

At first, he figured his legs must have fallen asleep. He pulled himself up, leaning on his desk, and slowly straightened until he was standing. He could feel the weight on his feet and knees. He let go of the desk and commanded his legs to move. Instead, they buckled, and he landed on the floor with a thud.

His brother awkwardly pulled him onto the bed. Then they waited. Surely this weird paralysis would disappear just as suddenly as it came. An hour passed, then two. I’m calling an ambulance, the younger brother announced finally. Reluctantly, the elder agreed. He was embarrassed to be this helpless but worried enough to want help.


When the E.M.T.s arrived, they were as confused as the brothers. The medics asked what the young man had been up to. Nothing bad, he assured them. For the past few weeks he had been getting back into shape. He changed his diet, cut out the junk and was drinking a protein concoction that was supposed to help him build muscle. And he was working out hard every day. He’d lost more than 20 pounds, he added proudly.

Hearing about this extreme diet and exercise regimen, the E.M.T.s told the man he was probably dehydrated. He needed fluids and some electrolytes. A couple of bottles of Gatorade and he would very likely feel a lot better. And if he didn’t, he could call again.

With his brother’s help, the man moved himself to a sitting position. He drank some water and Gatorade and waited to start feeling better. He fell asleep, still waiting. By the following afternoon he was having trouble sitting upright. He was drinking yet another Gatorade when he noticed that the bottle felt heavy. He realized with a start that the weakness had moved into his arms. Call the ambulance, he told his brother. This can’t be dehydration.

A new set of E.M.T.s agreed. They hoisted the weakened man onto a stretcher, fastened the straps tightly and headed down the stairs. The man felt himself pitch forward as the stretcher tilted down. Was he going to fall? He imagined himself tumbling down the stairs like a sack of potatoes, completely unable to protect himself. The straps held him on the stretcher, but that feeling of helplessness terrified him.

Dr. Getaw Worku Hassen was the emergency-medicine doctor on duty that night at Metropolitan Hospital in Upper Manhattan. He asked the patient if anything like this had happened before. No, the patient replied, though recently his thighs had felt tired and weak at times. It never lasted long, and he figured it was from working out so hard. The man asked if he might have had a stroke. Would he ever be able to walk again? Hassen reassured him that his symptoms didn’t look like a stroke. But, the doctor acknowledged, he wasn’t sure what it did look like.


On exam, the man’s heart was racing at 110 beats a minute. And his blood pressure was high. He couldn’t lift either leg off the stretcher — not even an inch. His arms were weak as well. But his reflexes, sensation and the rest of his nervous system seemed otherwise normal.

Hassen told the man that they would need to wait for the results of his blood work and other tests. He would be back when he knew more. Moments later the doct or was called by the lab. One of the patient’s electrolytes was dangerously low — his potassium.


Potassium is probably the most important electrolyte we measure routinely. It is essential for every cell in the body, and its movement in and out of cells is key to many of the body’s functions. Hassen immediately ordered potassium to be given both by mouth and intravenously. He wasn’t sure why this young man had such a low level of potassium but knew that if he didn’t get more, he could die. Cells in the heart depend on the flow of potassium to work properly. Either too much or too little of it could cause the heart to develop a life-threatening arrhythmia.

The patient was admitted to the intensive-care unit so that his heart could be monitored as the deficit was reduced. The patient says he could feel strength flowing back into his muscles almost as soon as he started getting the replacement electrolyte. By morning he felt strong enough to stand. By midafternoon, he could walk. The doctors gave him potassium tablets to take every day for the next week and told him to stay hydrated if he was going to keep up this fitness regimen. And, of course, he should follow up with his regular doctor.

A few days later, when Hassen returned to the hospital for his next shift, he wondered what had happened to the man with the weakened legs. He saw that his potassium had come back to a normal level and that he had been discharged. These days, financial pressures push doctors caring for hospitalized patients to narrow their focus to identifying life-threatening conditions and addressing those enough to stabilize the patient. Patients are then sent back to their primary-care doctors to determine the hows and whys behind the conditions that sent them to the hospital in the first place. Hassen accepted this reality, and yet to him the real pleasure of medicine wasn’t just identifying and addressing the serious symptoms but figuring out the cause behind the cause of the symptom. This man’s weakness was caused by low potassium. But what made his potassium low?


Hassen reviewed the notes from the patient’s overnight stay. In the emergency department, he had been weak, his heart racing, his blood pressure high and his potassium low. When electrolytes were repleted, his strength returned and his blood pressure dropped. But his heart continued to race. Heart rates are often high in the E.R.: Patients are scared and sometimes sick, often in pain. But this man’s heart rate stayed high even as everything else got better. That struck Hassen as strange.

And so Hassen turned to the internet. He eventually found a case report that bore a striking resemblance to his patient: a young man with weak legs, low potassium and a high heart rate. That patient turned out to have something Hassen had never heard of: thyrotoxic periodic paralysis, muscle weakness where the low potassium was being caused by an excess of thyroid hormone.

The thyroid is a gland located in the neck that helps control the body’s metabolic rate. Too much thyroid hormone causes the body to race. Too little, and it slows to a crawl. Unchecked, either state can be fatal. Rarely, in some people — usually young, often male — too much thyroid hormone can make circulating potassium levels drop and cause weakness.

Hassen called the lab. He ordered tests to check the level of thyroid hormone in the sample. It was very high. He called the patient and got no answer, and he had no way to leave a message. He called the number a dozen times over the course of the next few weeks. Finally, maybe accidentally, the patient picked up.

Hassen explained what he’d discovered. He gave the patient the name of an endocrinologist in the area. It turned out the young man had what is known as Graves’s disease. This is an autoimmune disease in which the patient’s own antibodies induce the thyroid gland to produce too much hormone. It’s often treated with radioactive iodine, which kills off some or most of the hormone-producing cells in the gland. This man, instead, chose to take a medicine that interferes with the gland’s ability to make thyroid hormone.


This diagnosis was made almost four years ago. The patient gave up his intensive diet and exercise regimen and is now trying just to stay in shape and eat smarter — and to take his medicine every day. Sometimes when he feels his thighs are tired or weak, he eats a banana or avocado to get the potassium that he thinks his body is craving. He is determined to never relive that kind of helplessness again.

Lisa Sanders, M.D., is a contributing writer for the magazine. Her latest book is ‘‘Diagnosis: Solving the Most Baffling Medical Mysteries.’’ If you have a solved case to share with Dr. Sanders, write her at [email protected]

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